1. Electron Configurations
Ch 4. Section 3

2. What do these mean?
Number of Electrons
1s22s22p2
Energy Level
Shape

3. Objective
List the total number of electrons needed to fully occupy each main energy level

4. Blocks of the Periodic table

5. Orbitals on the Periodic Table

6. Orbitals on the Periodic table

7. Bell Work: Review Of Scientist
Work with a group according to your seat number to find at least 2 things that were significant about your assigned scientist
1-4: Louis de Broglie
5-8: Werner Heisenberg
9-12: Niels Bohr
13-16: Max Planck
17-20: Albert Einstein
21-25: Erwin Schrödinger
When you are done write them on the large board on the wall and finish your Periodic Table of Electron Configurations

8. Objective
State the Aufbau principle, the Pauli exclusion principle, and Hund’s rule.

9. Aufbau Principle
An electron occupies the lowest-energy orbital it can achieve.
Each box represents an orbital
The order of increasing energy is on the vertical axis
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d

10. Pauli Exclusion Principle
+1/2
No two electrons in the same atom can have the same set of four quantum numbers.
The spin quantum number has two values either ± ½
Whether it is positive or negative tells us the spin
Tells us the more precise location of the electron
-1/2

11. Hund’s Rule 2p
Orbitals of equal energy are each occupied by one electron before any orbitals is occupied by a second electron, and all electrons in singly occupied orbitals must have same spin.
Now lets figure out the electron configuration for phosphorus
It has 15 electrons that must be accounted for

12. Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p
The first 2 e-’s go into the 1s orbital
Notice opposite direction of spins

13. Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p
The next two electrons go into the 2s orbital
Notice the opposite spin

14. Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p
The next six electrons go into the 2p orbital
Notice the opposite spin

15. Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p 3s 2p
The next two electrons go into the 3s orbital
Notice the opposite spin
Now we have 12 electrons and need to account for 3 more

16. Increasing energy = 1s22s22p63s23p3 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s
The next three electrons go into the 3p orbital
They each go into separate shapes (Hund’s)
3 unpaired e-’s
= 1s22s22p63s23p3

17. Representing Electron Configurations
Orbital Notation: The lines are labeled with the principal quantum number and sublevel letter. 1s He H 1s
Orbital with 2 electrons
Orbital with 1 electron

18. Representing Electron Configuration Continued
Electron-Configuration Notation:
Electron-configuration notation eliminates the lines and arrows of orbital notation.
Instead, the number of electrons in a sublevel is shown by adding a superscript to the sublevel designation.
He: 1s2
The superscript indicates that there are two electrons in helium’s 1s orbital.

19. Sample Problem A
The electron configuration of boron is 1s22s22p1. How many electrons are present in an atom of boron? What is the atomic number for boron? Write the orbital notation for boron.

20. Sample Problem A solution
The number of electrons in a boron atom is equal to the sum of the superscripts in its electron-configuration notation: = 5 electrons. The number of protons equals the number of electrons in a neutral atom. So we know that boron has 5 protons and thus has an atomic number of 5. To write the orbital notation, first draw the lines representing orbitals. 1s 2s 2p

21. Sample Problem A Solution
Next, add arrows showing the electron locations. The first two electrons occupy n = 1 energy level and fill the 1s orbital. 1s 2s 2p

22. Sample Problem A Solution
The next three electrons occupy the n = 2 main energy level. Two of these occupy the lower-energy 2s orbital. The third occupies a higher-energy p orbital. 1s 2s 2p

23. 4.3 Practice Problems
Textbook pg. 107: A. 1-2

24. Elements in the Second Period
In the first-period elements, hydrogen and helium, electrons occupy the orbital of the first main energy level.
According to the Aufbau principle, after the 1s orbital is filled, the next electron occupies the s sublevel in the second main energy level.

25. Terminology
The highest-occupied energy level is the electron- containing main energy level with the highest principal quantum number.
Inner-shell electrons are electrons that are not in the highest-occupied energy level.

26. Elements in the third period
After the outer octet is filled in neon, the next electron enters the s sublevel in the n = 3 main energy level.
Noble-Gas Notation
The Group 18 elements (helium, neon, argon, krypton, xenon, and radon) are called the noble gases.
A noble-gas configuration refers to an outer main energy level occupied, in most cases, by eight electrons.

27. Elements in the fourth Period
The period begins by filling the 4s orbital, the empty orbital of lowest energy.
With the 4s sublevel filled, the 4p and 3d sublevels are the next available vacant orbitals.
The 3d sublevel is lower in energy than the 4p sublevel. Therefore, the five 3d orbitals are next to be filled.

28. Elements in the fifth Period
In the 18 elements of the fifth period, sublevels fill in a similar manner as in elements of the fourth period.
Successive electrons are added first to the 5s orbital, then to the 4d orbitals, and finally to the 5p orbitals.

29. Notecard: Aufbau Diagram Order that orbitals fill
1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p6

30. Noble-Gas Notation 1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p6
The Group 18 elements (helium, neon, argon, krypton, xenon, and radon) are called the noble gases.
A noble-gas configuration refers to an outer main energy level occupied, in most cases, by eight electrons.
1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p6
1s22s22p63s23p6
[Ne]
1s22s22p63s23p64s23d104p6
[Ne]
[Ar]
1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p6
[Ne]
[Ar]
[Kr]
[Xe]
1s22s22p63s23p64s23d104p65s24d105p6
[Ne]
[Ar]
[Kr]
[Ne]
[Ar]
[Kr]
[Xe]
[Rn]
1s22s22p6

31. Sample Problem B
a. Write both the complete electron-configuration notation and the noble-gas notation for iron, Fe.
b. How many electron-containing orbitals are in an atom of iron? How many of these orbitals are completely filled? How many unpaired electrons are there in an atom of iron? In which sublevel are the unpaired electrons located?

32. Sample B Solution A Complete: 1s22s22p63s23p63d64s2 B
Noble Gas: [Ar]3d64s2 B
An iron atom has 15 orbitals that contain electrons.
one 1s orbital, one 2s orbital, three 2p orbitals, one 3s orbital, three 3p orbitals, five 3d orbitals, and one 4s orbital
11 orbitals are full
4 unpaired electrons in the 3d
The notation 3d6 represents 3d
one 4s orbital

33. 4.3 Practice Problems
Textbook:
A (p 107) Already Done
B (p. 115)

34. Sample Problem C
a. Write both the complete electron-configuration notation and the noble-gas notation for a rubidium atom.
b. Identify the elements in the second, third, and fourth periods that have the same number of highest-energy-level electrons as rubidium.

35. Sample Problem C Solution
1s22s22p63s23p63d104s24p65s1
[Kr]5s1 B
Rubidium has one electron in its highest energy level (the fifth). The elements with the same outermost configuration are,
in the second period, lithium, Li;
in the third period, sodium, Na;
and in the fourth period, potassium, K.

36. Exceptions to Aufbau principle
Lowest energy to higher energy.
Adding electrons can change the energy of the orbital. Full orbitals are the absolute best situation.
However, half filled orbitals have a lower energy, and are next best
Makes them more stable.
Changes the filling order

37. Look At these configurations
Titanium - 22 electrons
1s22s22p63s23p64s23d2
Vanadium - 23 electrons
1s22s22p63s23p64s23d3
Chromium - 24 electrons
1s22s22p63s23p64s23d4 (expected)
**But this is not what happens!!**

38. Chromium is actually 1s22s22p63s23p64s13d5 Why?
This gives us two half filled orbitals (the others are all still full)
Half full is slightly lower in energy.
The same principal applies to copper.

39. Copper Remember these exceptions: d4, d9 1s22s22p63s23p64s23d9
Copper has 29 electrons so we expect:
1s22s22p63s23p64s23d9
But the actual configuration is:
1s22s22p63s23p64s13d10
This change gives one more filled orbital and one that is half filled.
Remember these exceptions: d4, d9

40. 4.3 Practice Problems
Textbook: A. 1-2 (p 107) Already Done B. 1-4 (p. 115) Already Done C. 1-2 (p. 116)